1. Field of the Invention
The present invention relates to apparatus and a method of separating hydrocarbons from mixtures with water, in particular hydrocarbon/water/emulsifier mixtures recovered from wellbore fluids in remediation processes.
2. Related Information
Due to environmental concerns the removal of volatile material from solids has become an important process. For example, volatile materials must be removed from solids in the reclamation of petroleum lubricated drilling fluids used in the exploration and production of petroleum oils. The drilling fluid, referred to as "mud", serves several purposes, the most important of which includes cooling and lubricating the bit and removing drilled solids, or cuttings, from the borehole. While most mud is a water based, flowable composition, the drilling mud is frequently compounded with a lubricant material such as diesel, crude oil or other non-water petroleum based constituent and various surfactants or emulsifiers to create stable emulsions of the water and hydrocarbon to facilitate the mud's lubricating characteristics.
The mud may be contained in a mud tank, which is connected by way of a mud line and mud pump to a hose and swivel used to inject the mud into the top of the drill pipe. The returning mud, combined with the cuttings, is captured in a mud return pipe and recirculated through the drill pipe.
When the concentration of the drill cuttings in the mud rises too high recirculation of the mud becomes a problem. In order for the mud to perform its several functions, its viscosity, density and other properties must be maintained within acceptable limits. The drill cuttings adversely affect these properties thus reducing the carrying capacity of the mud and damaging the drilling equipment.
To allow for effective recirculation, the mud is usually separated from the cuttings prior to being recycled through the drill string. The cuttings are then disposed of as waste which presents a problem when the lubricating properties of the mud have been enhanced by the addition of hydrocarbons. Because of the hydrocarbons in the cuttings a hazardous waste problem is presented. Historically, the contaminated cuttings were diluted by mixing and hauled to remote sites for disposal in landfills. This, however, also presents a problem in that the landfill then becomes a "hazardous" waste site leaving the dumper liable for environmental damages indefinitely.
Decontaminating the cuttings is more attractive. Treatment processes heretofore available to remove oil or other hydrocarbons from cuttings include distillation, solvent washing, and mud burning. While these processes are effective to varying degrees at stripping the hydrocarbon contaminants from cuttings, rendering the cuttings environmentally clean, they remain problematic in that disposal persists with the liquid or vapor from the disassociated contaminant.
There are several patents on rotary kilns specifically designed to remove volatile hydrocarbons from solid material such as soil. See for example U.S. Pat. Nos. 5,152,233; 5,199,354; 5,302,118; and 5,378,059. All of the rotary kilns are gas fired with the hot combustion gases being directed into the drum to heat the solids. When the solids have a substantial quantity of hydrocarbonaceous material an explosion hazard may be present. In addition, when the flame is applied directly to the contaminated materials, the solids are burned so that the contaminants are consumed and turned into smoke which may be an environmental hazard.
In order to achieve remediation, it has been determined that the hydrocarbons and water extracted with the cuttings from the wellbore fluid must be separated to recycle the materials or recover them for other disposition. One would normally expect that phase separation of the water and oil would be easily accomplished. However, when hydrocarbons such as diesel are incorporated in the water, surfactants or other emulsifiers must be added to obtain stable emulsion of the water/oil mixtures during use in the wellbore. These emulsifiers are volatilized out of the kiln along with the water and hydrocarbons, resulting in a recovered material, which when condensed is again a stable emulsion of water and oil.
One feature of this invention is to provide an apparatus to receive volatile contaminants from solids to recover and/or recycle the disassociated hydrocarbons. It is a particular feature that the present invention provides a process to separate water from hydrocarbons without the formation of stable emulsions thereof.